Phosphate Binding to Isolated Chloroplast Coupling Factor (CF^

Bernhard Huchzermeyer Botanisches Institut, Tierärztliche Hochschule, Bünteweg 17d, D-3000 Hannover 71, Bundesrepublik Deutschland Z. Naturforsch. 43c, 213-218 (1988); received July 27/November 19, 1987 Chloroplast, Coupling Factor, Binding Sites, ATPase, Phosphorylation A single binding site for phosphate was found on isolated chloroplast coupling factor in the absence of nucleotides. In our experiments the phosphate binding site showed a Kd of 170 JIM. We did not observe any differences whether the ATPase activity of CF] had been activated or not. If the enzyme was incubated with [y-P]ATP the amount of P bound per CF, depended on the pretreatment of the enzyme: In the presence of ADP no ATP or phosphate was bound to CF,. After activation of ATPase activity one mol of ATP per mol CF, was rapidly bound and hydrolyzed while there was a slowly occurring binding of another phosphate without concomitant nucleotide binding. We conclude that there are two different types of phosphate binding observed in our experiments: 1) Inorganic phosphate can be bound by one catalytic site per mol of CTv 2) The yphosphate of ATP is able to bind to an ATP binding domain of the enzyme if this domain can exchange substrates with the incubation medium. This ATP binding domain appears to differ from the site binding inorganic phosphate, because at least a portion of the coupling factor contains more than one labelled phosphate during our ATPase tests.